JP2007027415A - Magnetic storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce erroneous writing and improve thermal stability. <P>SOLUTION: A magnetic storage device is provided with a magneto-resistance effect element 10 including a fixed layer 11, a recording layer 13 and a non-magnetic layer 12; and a first wiring 15 extending in a first direction and used for generating a magnetic field for recording information into the recording layer 13 of the element 10. The recording layer 13 has an extending section 10a extending in a second direction rotated so as to form an angle of 0-20 degrees for the first direction, and provided with first and second side surfaces facing with each other and each extending in the second direction and third and fourth side surfaces opposite to each other; and first and second projection sections 10b, 10c projecting from the first and second side surfaces in a third direction perpendicular to the second direction. The third and fourth side surfaces are each inclined in a rotation direction in which the extending section 10a rotates in the third direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic memory device, and more particularly to a magnetic memory device using a magnetoresistive element as a memory cell.

  Conventionally, various types of magnetic memories have been proposed. In recent years, magnetic random access memory (MRAM) using a magnetoresistive element exhibiting a giant magnetoresistive (GMR) effect has been proposed, and in particular, magnetism using a ferromagnetic tunnel junction is proposed. Attention has been focused on random access memory.

  The ferromagnetic tunnel junction is composed of, for example, a first ferromagnetic layer, an insulating layer, and a second ferromagnetic layer, and a current flows through the insulating layer. In this case, the junction resistance value changes according to the cosine of the relative angle in the magnetization direction of the first and second ferromagnetic layers. Therefore, the junction resistance value has a minimum value when the magnetization directions of the first and second ferromagnetic layers are parallel, and has a maximum value when the magnetization directions are antiparallel. This is called a tunneling magnetoresistive (TMR) effect, and a change in junction resistance value due to the TMR effect may exceed 70% at room temperature.

  In a memory cell including a ferromagnetic tunnel junction, at least one ferromagnetic layer is regarded as a reference layer, its magnetization direction is fixed, and the other ferromagnetic layer is used as a recording layer. In this memory cell, information is recorded by associating binary information ("0", "1") with the magnetization directions of the reference layer and the recording layer being parallel or antiparallel. When recording information is written into the memory cell, the magnetization direction of the recording layer is reversed by a magnetic field generated by passing a current through a write wiring provided separately for the memory cell.

  Further, reading of recorded information from the memory cell is performed by passing a current through the ferromagnetic tunnel junction and detecting a change in resistance value due to the TMR effect. A magnetic memory is configured by arranging a large number of such memory cells. The actual configuration is configured by arranging a switching transistor for each cell and incorporating a peripheral circuit, for example, like a DRAM (Dynamic Random Access Memory) so that an arbitrary cell can be selected. In addition, a method of incorporating a ferromagnetic tunnel junction in combination with a diode at a position where a word line and a bit line intersect has been proposed (see Patent Document 1 and Patent Document 2).

  In order to operate an MRAM using a memory cell including a ferromagnetic tunnel junction, it is indispensable to eliminate erroneous writing to unselected cells. In the MRAM, information is written to the recording layer by applying a synthetic magnetic field of a magnetic field Hx in the easy axis direction and a magnetic field Hy in the hard axis direction to a selected memory cell. At this time, no magnetic field is applied to the non-selected memory cells, or a magnetic field only in a single direction is applied. Here, a memory cell to which a magnetic field is applied in a single direction is referred to as a half-selected memory cell.

  Here, the magnetization reversal characteristic in the simultaneous rotation model is represented by an asteroid curve. In this asteroid curve, the switching magnetic field Hsw necessary for the magnetization reversal when the magnetic field is applied in the easy axis direction and the hard axis direction is more than the easy axis switching magnetic field Hc when the magnetic field is applied only in the easy axis direction. Get smaller. At this time, the unidirectional magnetic field Hx necessary for writing information to the selected memory cell can be set to be smaller than Hc. Ideally, erroneous writing to the half-selected memory cell does not occur. However, since there is a variation in the reversal magnetic field in an actual memory cell, erroneous writing to the half-selected memory cell may occur unless Hsw is made sufficiently smaller than Hc.

  On the other hand, since the magnetic random access memory operates as a non-volatile memory, it must be able to hold recorded information stably. There is a parameter called a thermal fluctuation constant as a standard for recording information stably for a long time, and it is generally said that this thermal fluctuation constant is proportional to the volume of the recording layer and Hsw. Therefore, if Hsw is reduced to reduce erroneous writing, the thermal stability is similarly reduced, and information cannot be held for a long time.

  In view of the above, it is important to propose a magnetoresistive element capable of retaining information for a long period of time by increasing thermal stability while reducing Hsw. Become.

As a related technique of this type, a technique for improving the write characteristics by correcting the magnetization pattern of the magnetoresistive element is disclosed (see Patent Document 3).
US Pat. No. 5,640,343 US Pat. No. 5,650,958 Japanese Patent No. 3548036

  The present invention provides a magnetic storage device capable of reducing erroneous writing and improving thermal stability.

  A magnetic storage device according to one aspect of the present invention includes a fixed layer whose magnetization direction is fixed, a recording layer whose magnetization direction changes, and a nonmagnetic layer provided between the fixed layer and the recording layer. A magnetoresistive effect element; and a first wiring that extends in a first direction and generates a magnetic field for recording information in the recording layer of the magnetoresistive effect element, the recording layer comprising: The first direction extends in a second direction rotated so as to form an angle greater than 0 degrees and not more than 20 degrees with respect to the first direction, and is opposed to each other and extends in the second direction. And an extended portion having a third side and a fourth side opposite to the second side, and a third direction perpendicular to the second direction from the first and second sides, respectively. A first projecting portion projecting from the second projecting portion, and the third and fourth side surfaces projecting from the third projecting portion; The extending portion is inclined respectively in the rotational direction to rotate with respect to the direction.

  According to the present invention, it is possible to provide a magnetic storage device capable of reducing erroneous writing and improving thermal stability.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, elements having the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

  The inventors of the present invention manufactured an MTJ (Magnetic Tunnel Junction) element which is an example of a magnetoresistive effect element as described below in order to reduce erroneous writing and increase the yield.

  FIG. 1 is a plan view showing an embodiment of an MTJ element 10 according to the present invention. FIG. 2 is a cross-sectional view of the MTJ element shown in FIG. 2 shows a cross-sectional view along the X direction shown in FIG. 1, for example.

  As shown in FIGS. 1 and 2, an MTJ element 10 according to an embodiment of the present invention includes at least a fixed layer (pinned layer) 11 with a fixed magnetization direction and a recording layer (free layer) with a reversed magnetization direction. ) 13 and a nonmagnetic layer (for example, a tunnel insulating layer) 12 sandwiched between the fixed layer 11 and the recording layer 13. Furthermore, an antiferromagnetic layer 14 for fixing the magnetization of the fixed layer 11 is provided under the fixed layer 11.

  The MTJ element 10 includes an extending portion 10a extending in the X direction and protruding portions 10b protruding in the Y direction (direction perpendicular to the X direction) from, for example, the vicinity of both sides of the extending portion 10a. , 10c, and has a so-called cross shape. In other words, in the planar shape of the MTJ element 10, the width W1 in the Y direction near the center is wider than the width W2 in the Y direction at the end. In the case of the shape of FIG. 1, the X direction that is the extending direction of the extending portion 10 a is the easy axis direction of the MTJ element 10, and the Y direction that is the protruding direction of the protruding portions 10 b and 10 c is the MTJ element. This is the direction of 10 hard axes.

  It is desirable that the protruding portions 10b and 10c protrude from the side surface near the center of the extending portion 10a. However, it is not limited to this, The protrusion parts 10b and 10c may be provided in the asymmetrical position with respect to the extension part 10a. Further, the corners of the protruding portions 10b and 10c may be angular or rounded. That is, the influence on the asteroid curve of the MTJ element 10 is small depending on whether the corners of the protrusions 10b and 10c are angular or round.

  The planar shape of the extending portion 10a is, for example, a quadrangle, and two adjacent side surfaces are not perpendicular. That is, one of the two pairs of diagonals (angles A and C) is an acute angle, and the other pair of diagonals (angles B and D) is an obtuse angle. Note that, of the four side surfaces of the extending portion 10a, two opposing side surfaces on which the protruding portions 10b and 10c are provided are parallel to each other, for example, in the extending direction (X direction) of the extending portion 10a. Are also parallel.

  Of the four side surfaces of the extending portion 10a, the two opposing side surfaces where the projecting portions 10b and 10c are not necessarily required to be parallel. That is, the two side surfaces may be inclined in the same direction with respect to the hard axis direction. Further, the four corners A, B, C, and D of the extending portion 10a may be angular or rounded. FIG. 1 shows an MTJ element 10 including an extending portion 10a whose planar shape is a parallelogram.

  In other words, the planar shape of the MTJ element 10 has a 180-degree rotational symmetry (or two-fold rotational symmetry) and does not have a mirror symmetry. In the MTJ element 10 shown in FIGS. 1 and 2, the fixed layer 11, the nonmagnetic layer 12, the recording layer 13, and the antiferromagnetic layer 14 are all in the same planar shape, but only the recording layer 13 has the shape described above. You may have.

  The aspect ratio L / W of the MTJ element 10 is set to be larger than 1. The aspect ratio L / W of the MTJ element 10 is preferably 1.5 to 2.2. This is calculated in consideration of the variation of the easy axis switching magnetic field Hc, and in the case of the aspect ratio in the above range, the variation of the magnetic field Hc can be reduced. The aspect ratio L / W of the MTJ element 10 is defined as follows. That is, taking the planar shape of FIG. 1 as an example, the maximum length in the X direction is L, the maximum width in the Y direction is W, and L / W is defined as the aspect ratio.

  Here, in the case of the MTJ element 10 having the shape shown in the figure, the length L is the maximum distance when the side surfaces of both ends in the X direction in the extending portion 10a are connected in the X direction (magnetization easy axis direction). . The width W is the maximum distance when the side surface of the end portion in the Y direction of the protruding portion 10b and the side surface of the end portion in the Y direction of the protruding portion 10c are connected in the Y direction (hard magnetization direction). In other words, when the corners of the extending portion 10a made of a parallelogram are A, B, C, and D, the length L is the midpoint Mab of the side AB connecting the corners A and B and the corner C. And a distance connecting the midpoint Mcd of the side CD connecting the corner D.

Next, an example of the material of the MTJ element 10 will be described. The following ferromagnetic materials are used for the material of the fixed layer 11 and the recording layer 13. For example, Fe, Co, Ni, a laminated film thereof, or an alloy thereof, magnetite having a high spin polarizability, an oxide such as CrO ₂ , RXMnO _{3 -Y} (R: rare earth, X: Ca, Ba, Sr) In addition, it is preferable to use Heusler alloys such as NiMnSb and PtMnSb. In addition, these magnetic materials include Ag, Cu, Au, Al, Mg, Si, Bi, Ta, B, C, O, N, Pd, Pt, Zr, Ir, W, and Mo as long as ferromagnetism is not lost. , Nb and other nonmagnetic elements may be included.

As the material of the antiferromagnetic layer 14, for example, Fe—Mn, Pt—Mn, Pt—Cr—Mn, Ni—Mn, Ir—Mn, NiO, Fe ₂ O ₃ or the like is preferably used.

For the material of the nonmagnetic layer 12, various dielectrics such as Al ₂ O ₃ , SiO ₂ , MgO, AlN, Bi ₂ O ₃ , MgF ₂ , CaF ₂ , SrTiO ₂ , and AlLaO ₃ may be used. it can. These dielectrics may have oxygen, nitrogen, or fluorine deficiency.

  Next, an asteroid curve of the MTJ element 10 configured as described above will be described. FIG. 3 is a plan view showing the main part of the MRAM including the MTJ element 10 shown in FIG. The first write wiring 15 is provided so as to extend in the X direction. The second write wiring 16 is provided so as to extend in the Y direction. The first write wiring 15 applies a magnetic field in the Y direction to the MTJ element 10. The second write wiring 16 applies a magnetic field in the X direction to the MTJ element 10.

  The MTJ element 10 is disposed in an intersection region between the first write wiring 15 and the second write wiring 16. Specifically, the easy axis of magnetization of the MTJ element 10 is substantially parallel to the first write wiring 15. Further, the hard axis of magnetization of the MTJ element 10 is substantially parallel to the second write wiring 16.

  FIG. 4 is a diagram showing an asteroid curve of the MTJ element 10 shown in FIG. Here, a writing magnetic field (synthetic magnetic field in the direction of easy axis of magnetization and the direction of hard axis of magnetization) necessary for magnetization reversal at a point P where the straight line L inclined by 45 degrees from the X axis and the asteroid curve intersect is defined as a switching magnetic field Hsw. Further, a write magnetic field necessary for magnetization reversal only in the easy axis direction (that is, a magnetic field at the point where the asteroid curve and the X axis intersect) is defined as an easy axis switching magnetic field Hc.

  The magnetic field Hsw required for magnetization reversal when a magnetic field is applied in the easy axis direction and the hard axis direction is smaller than the magnetic field Hc when a magnetic field is applied only in the easy axis direction. At this time, the unidirectional magnetic field Hx necessary for writing information to the selected memory cell can be set to be smaller than Hc. Ideally, erroneous writing to the half-selected memory cell does not occur. However, since there is a variation in the reversal magnetic field in an actual memory cell, erroneous writing to a half-selected memory cell may occur unless Hsw is made sufficiently smaller than Hc.

  As shown in FIG. 4, it can be seen that the MTJ element 10 having the shape shown in FIG. 1 has a sufficiently high Hc with respect to Hsw, and has improved write margin and thermal stability.

  However, when the vicinity of the X axis of the asteroid curve is viewed in detail, asymmetry occurs in the asteroid shape between the first quadrant and the second quadrant. Further, the point Q at which the asteroid curve closes when a magnetic field is applied in the Y-axis direction is deviated from the Y-axis. This is undesirable because it reduces the write margin.

(First embodiment)
FIG. 5 is a plan view showing a main part of the MRAM including the MTJ element 10 according to the first embodiment of the present invention. In the first embodiment, the MTJ element 10 of the first example having the same shape as the MTJ element described with reference to FIGS. 1 and 2 is used.

  The first write wiring 15 is provided so as to extend in the X direction. The second write wiring 16 is provided so as to extend in the Y direction perpendicular to the X direction. The first write wiring 15 applies a magnetic field in the Y direction to the MTJ element 10. The second write wiring 16 applies a magnetic field in the X direction to the MTJ element 10. Each of the first write wiring 15 and the second write wiring 16 may be provided with a predetermined distance from the MTJ element 10 or may be electrically connected to the MTJ element 10.

  The MTJ element 10 is disposed in an intersection region between the first write wiring 15 and the second write wiring 16. In addition, the MTJ element 10 is arranged such that the easy axis of magnetization is inclined, for example, 5 degrees (°) with respect to the extending direction of the first write wiring 15 (that is, the X direction) (or rotated by 5 degrees). Has been. In other words, the MTJ element 10 is arranged such that the hard axis is inclined by, for example, 5 degrees with respect to the extending direction of the second write wiring 16 (that is, the Y direction).

  In addition, the MTJ element 10 is rotated in such a manner that two opposing side surfaces of the four side surfaces of the extending portion 10a that are not provided with the protruding portions 10b and 10c are inclined with respect to the hard axis direction (or rotated). ) Direction.

  FIG. 6 is a diagram showing an asteroid curve of the MTJ element 10 shown in FIG. FIG. 5 shows an asteroid curve (that is, the MTJ element 10 shown in FIG. 3) when the easy magnetization axis and the first write wiring 15 as a comparative example are substantially parallel (rotation angle 0 degree). Steroid curve) is also shown.

  As shown in FIG. 6, when the asteroid curve near the X axis is compared between 0 degree and 5 degrees, asymmetry of the asteroid curve between the first quadrant and the second quadrant is obtained by rotating 5 degrees. Is getting smaller. Thereby, the write margin of the MTJ element 10 can be improved.

  Further, when comparing the asteroid curve near the Y axis between 0 degree and 5 degrees, by rotating the MTJ element 10 by 5 degrees, the magnetic field is applied in the Y axis direction and the point Q is closed. , And substantially coincide with the Y axis. That is, even in the asteroid curve near the Y axis, the asymmetry between the first quadrant and the second quadrant is small.

  Next, the easy axis switching magnetic field Hc and the variation σHc of the magnetic field Hc when the rotation angle of the MTJ element 10 is changed will be described.

  FIG. 7 is a diagram showing the rotation angle dependence of the magnetic field Hc in the MTJ element 10. The horizontal axis represents the rotation angle (degrees). The vertical axis represents the ratio of Hc to Hc0. Hc0 represents Hc when the rotation angle is 0 degree. That is, in FIG. 7, the magnetic field Hc is normalized by the easy axis switching magnetic field Hc0 of the MTJ element 10 at a rotation angle of 0 degree.

  As shown in FIG. 7, when the rotation angle of the MTJ element 10 is changed in the range from 0 degree to 20 degrees, it can be seen that the magnetic field Hc hardly changes in this range. That is, in the range of at least 0 degrees to 20 degrees, Hc is sufficiently large with respect to Hsw, and the effects of improving the write margin and thermal stability are the same as in the case of the rotation angle of 0 degrees.

  FIG. 8 is a diagram showing the rotation angle dependence of the variation σHc of the magnetic field Hc in the MTJ element 10. The horizontal axis represents the rotation angle (degrees). The vertical axis represents the ratio of σHc to σHc0. σHc0 represents σHc when the rotation angle is 0 degree. That is, in FIG. 8, the variation σHc is normalized by the variation σHc0 of the MTJ element 10 at a rotation angle of 0 degree. FIG. 9 shows specific numerical values at the rotation angles 0 degree, 2 degrees, 5 degrees, 10 degrees and 20 degrees of the curve shown in FIG.

  As shown in FIG. 8, it can be seen that when the MTJ element 10 is rotated, the value of σHc / σHc0 decreases. In addition, the value of σHc / σHc0 rapidly decreases in the range where the rotation angle is greater than 0 degree and 2 degrees or less, and the value of σHc / σHc0 is minimum at the rotation angle of 2 degrees.

  If the value of σHc / σHc0 is smaller than 1, the variation σHc is reduced and the write margin is improved. That is, if the rotation angle is greater than 0 degree and 20 degrees or less, the variation σHc can be reduced.

  Further, if the rotation angle is larger than 0 degree and 15 degrees or less, the variation σHc is reduced by 10% or more. Therefore, in this range, the effect of reducing the variation σHc is great. When the rotation angle is 10 degrees, the variation σHc is larger than 10% (specifically, 0.88) and is reduced. In the case of the rotation angle of 5 degrees, the variation σHc is reduced to 0.87. Therefore, it is most desirable that the rotation angle is larger than 0 degree and 5 degrees or less.

  As described above in detail, according to this embodiment, the switching magnetic field Hc in the X-axis direction can be sufficiently increased with respect to Hsw. As a result, the write margin can be improved and the thermal stability can be improved, so that erroneous writing to the MTJ element 10 can be reduced.

  Further, the variation σHc of the magnetic field Hc can be reduced without reducing the magnetic field Hc. As a result, the yield of the MTJ element 10 can be increased.

  In addition, when the inclination (the rotation angle of the two side surfaces with respect to the hard axis of magnetization) of the two opposing side surfaces where the projecting portions 10b and 10c are not provided among the four side surfaces of the extending part 10a is changed, The Hsw of the asteroid curve also changes. However, even when the rotation angle of the two side surfaces changes, the asymmetry of the asteroid curve hardly changes. Therefore, even if this embodiment is applied to the MTJ element 10 in which the rotation angles of the two side surfaces are changed, the same effect can be obtained.

  Further, as described above, the MTJ element 10 may be configured so that only the recording layer 13 has the extending portion 10a and the protruding portions 10b and 10c. That is, the asteroid curve of the MTJ element 10 is almost determined by the planar shape of the recording layer 13. Therefore, the planar shapes of the fixed layer 11, the nonmagnetic layer 12, and the antiferromagnetic layer 14 are not particularly limited, and may be, for example, a quadrangle.

(Second Embodiment)
The MTJ element 10 used in the first embodiment is not limited to the shape shown in FIG. 1 and can be variously modified. In the present embodiment, another shape of the MTJ element 10 will be described. These MTJ elements 10 are used by rotating the easy magnetization axis at an angle greater than 0 degree and 20 degrees or less with respect to the extending direction of the first write wiring 15 as in the first embodiment. Of course.

  FIG. 10 is a plan view showing a second example of the MTJ element 10. The extending part 10a is, for example, a parallelogram. The protrusions 10b and 10c each have a rounded corner. Further, each of the protruding portions 10b and 10c may be rounded only at the corners or may be rounded as a whole from the root as shown in FIG. In other words, the rounding size (specifically, the radius of curvature (the size of the radius R of a circle including a corner curve)) is not particularly limited. Moreover, the corner | angular shape of the protrusion parts 10b and 10c may be lacking without rounding. The aspect ratio of the MTJ element 10 shown in FIG. 10 is the same as the aspect ratio of the MTJ element 10 shown in FIG.

  FIG. 11 is a plan view showing a third example of the MTJ element 10. The MTJ element 10 shown in FIG. 11 is obtained by reducing the aspect ratio of the MTJ element 10 shown in FIG. However, the condition that the aspect ratio is 1 or more is satisfied. As described above, the MTJ element 10 having a small aspect ratio can be used.

  FIG. 12 is a plan view showing a fourth example of the MTJ element 10. The extending portion 10a has rounded corners. The radius of curvature of the corner is not particularly limited. Further, the corners of the extending part 10a may be in a chipped shape without being rounded. The protrusions 10b and 10c have rounded corners, for example. Further, the protrusions 10b and 10c may have angular corners. Actually, it is difficult to form the MTJ element 10 having all the corners as shown in FIG. 1 due to the etching accuracy in the manufacturing process, and the MTJ element 10 shown in FIG. 12 can be used. It can be said that the nature is high. The length L of the MTJ element 10 shown in FIG. 12 is also defined by the distance connecting the midpoint Mab of the side AB of the extending portion 10a and the midpoint Mcd of the side CD.

  FIG. 13 is a plan view showing a fifth example of the MTJ element 10. Of the four side surfaces of the extending portion 10a, the two opposing side surfaces where the protruding portions 10b and 10c are not provided rotate in the same direction with respect to the hard axis direction. The two side surfaces have different rotation angles with respect to the hard axis direction.

  In other words, one of the two sets of diagonals is an acute angle, and the other of the other diagonals is an obtuse angle. The two acute angles A and C are different from each other. Similarly, the two angles B and D that are obtuse angles are different from each other. Further, the extended portion 10a has, for example, rounded corners. The protrusions 10b and 10c have rounded corners, for example.

  FIG. 14 is a plan view showing a sixth example of the MTJ element 10. The radii of curvature of the two corners A and C, which are acute angles of the extending portion 10a, are different from each other. That is, one of the two corners A and C that is an acute angle is rounder than the other corner C. The protrusions 10b and 10c have rounded corners, for example.

  Even when the MTJ element 10 of the plurality of examples described above is used and the MTJ element 10 is rotated and arranged, the same effect as that of the first embodiment can be obtained. Of course, only the recording layer 13 of the MTJ element 10 may have the above shape.

  Next, a manufacturing method for manufacturing the MTJ element 10 will be described.

[1] Production method example 1
In the manufacturing method example 1, a manufacturing method of the MTJ element 10 having a general size will be described.

  First, an MTJ material layer is formed by sputtering, and a resist is applied on the MTJ material layer. Then, a pattern is formed using any of light, electron beam, and X-ray, and developed to form a resist pattern. Using this resist pattern as a mask, the MTJ material layer is ion milled or etched to form the MTJ element 10 having a desired shape. Thereafter, the resist is peeled off.

[2] Production method example 2
In the manufacturing method example 2, a manufacturing method of the MTJ element 10 having a relatively large size, for example, a micron order will be described.

  First, an MTJ material layer is formed by sputtering. Next, a hard mask made of, for example, silicon oxide or silicon nitride is formed on the MTJ material layer. Then, the hard mask is etched by a reactive ion etching (RIE) method to form a hard mask pattern having a desired shape. Using this hard mask pattern, the MTJ material layer is ion milled to form the MTJ element 10 having a desired shape.

[3] Production method example 3
In manufacturing method example 3, a manufacturing method of a smaller element, for example, an MTJ element 10 having a submicron size of about 2 to 3 μm to about 0.1 μm will be described. Photolithography can be used for processing the MTJ element having such a size as follows.

  First, an MTJ material layer is formed by sputtering. Next, a hard mask made of, for example, silicon oxide or silicon nitride is formed on the MTJ material layer. Then, the hard mask is etched by the RIE method to form a hard mask pattern having a desired shape. Using this hard mask pattern as a mask, the MTJ material layer is etched using the RIE method to form the MTJ element 10 having a desired shape.

[4] Production method example 4
In Manufacturing Method Example 4, a manufacturing method of the MTJ element 10 having a smaller size, for example, a size of about 0.5 μm or less will be described. Electron beam exposure can be used for processing such a very small MTJ element.

  However, in this case, since the element itself is very small, the shape part for expanding the edge domain region in one embodiment of the present invention is further reduced, so that it is very difficult to manufacture the MTJ element 10.

  Therefore, in order to manufacture the MTJ element 10 having a desired shape according to an embodiment of the present invention, proximity effect correction (OPC: Optical Proximity Correction) of an electron beam is used. This proximity effect correction is usually used to correct a proximity effect in a figure caused by backscattering of the electron beam from the substrate and form a correct pattern. This proximity effect correction is performed as follows, for example. For example, when a rectangular pattern is formed, there is a phenomenon that the amount of accumulated charge is insufficient near the vertex of the rectangle and the vertex of the rectangle is rounded. In order to clarify this apex, a normal pattern can be obtained by driving the correction point beam outside the figure in the vicinity of the apex, especially in the case of an element of about 0.5 μm or less, and increasing the accumulated charge amount. .

  In this manufacturing method example 4, using the method for correcting the proximity effect of the electron beam described above, a shape in which the width of the element end portion is widened is formed as follows. For example, when forming a so-called cross shape, a rectangular shape is used as a basic pattern, and a correction point beam is driven in the vicinity of two opposing vertices, whereby a shape having a wide element end can be formed. At this time, as compared with the case of normal proximity effect correction, the amount of electric charge to be applied is increased, or the position of the correction point beam is appropriately adjusted, or both of them are used to restore the shape more than recovering the vertex. It is good to correct (for example, sharpen a corner). Further, for example, a plurality of correction point beams can be irradiated to form a so-called cross shape.

(Third embodiment)
The third embodiment shows a configuration example of an MRAM using the MTJ element 10.

  The above-described MTJ element 10 is suitable for use as a memory element of a memory cell in MRAM. In general, in an MRAM using a magnetic material as a recording layer, there is no erroneous writing to adjacent cells, and even when the memory cell is miniaturized, it has a thermally stable recording layer to retain recorded information for a long period of time. Is required. Therefore, by using the MTJ element 10 according to one embodiment of the present invention described above, it is possible to provide a memory cell that can reduce the switching magnetic field and has a sufficiently large thermal fluctuation constant. As a result, the write current required for writing the memory bit can be reduced.

  Here, an example of a memory cell structure of the MRAM, [1] selection transistor type, [2] selection diode type, and [3] crosspoint type will be described.

[1] Selection Transistor Type FIG. 15 is a circuit diagram showing a selection transistor type MRAM according to the third embodiment of the present invention. FIG. 16 is a plan view showing the configuration of the select transistor type MRAM shown in FIG. FIG. 17 is a cross-sectional view showing the memory cell MC of the select transistor type MRAM shown in FIG. In FIG. 16, only the bit line (BL), the word line (WWL), and the MTJ element 10 are shown for simplification. In FIG. 17, the space between the semiconductor substrate 21 and the bit line (BL) 28 is filled with an insulating layer (not shown).

  One memory cell MC of the select transistor type includes one MTJ element 10, a transistor (for example, a MOS transistor) Tr connected to the MTJ element 10, a bit line (BL) 28, a word line (WWL) 26, It is comprised including. The memory cell array MCA is configured by arranging a plurality of memory cells MC in an array. Note that the word line (WWL) 26 corresponds to the first write wiring 15 shown in FIG. 5, and the bit line (BL) 28 corresponds to the second write wiring 16 shown in FIG.

  Specifically, one end of the MTJ element 10 is connected to one end (drain diffusion layer) 23a of the current path of the transistor Tr via the base metal layer 27, the contact plugs 24a, 24b, 24c and the wiring layers 25a, 25b. ing. On the other hand, the other end of the MTJ element 10 is connected to the bit line 28. A write word line (WWL) 26 that is electrically separated from the MTJ element 10 is provided below the MTJ element 10. The other end (source diffusion layer) 23b of the current path of the transistor Tr is connected to, for example, the ground potential via the contact plug 24d and the wiring layer 25c. The gate electrode 22 of the transistor Tr functions as a read word line (RWL).

  Note that one end of the MTJ element 10 on the base metal layer 27 side is, for example, the fixed layer 11 and the other end of the MTJ element 10 on the bit line 28 side is, for example, the recording layer 13. Absent. Further, for example, a hard mask may be interposed between the MTJ element 10 and the bit line 28.

  Further, as shown in FIG. 16, the MTJ element 10 is arranged so that the easy axis of magnetization is inclined by, for example, 5 degrees (or rotated by 5 degrees) with respect to the extending direction of the word line (WWL) 26. Yes. In other words, the MTJ element 10 is arranged such that the hard axis of magnetization is inclined by, for example, 5 degrees with respect to the extending direction of the bit line (BL) 28. As the MTJ element 10, for example, an element having the planar shape shown in FIG. 12 is used.

  In the select transistor type memory cell MC as described above, data write and read operations are performed as follows.

  First, the write operation is performed as follows. The bit line 28 and the write word line 26 corresponding to the selected MTJ element 10 among the plurality of MTJ elements 10 are selected. When write currents Iw1 and Iw2 are supplied to the selected bit line 28 and write word line 26, respectively, a combined magnetic field H by the write currents Iw1 and Iw2 is applied to the MTJ element 10. As a result, the magnetization direction of the recording layer 13 of the MTJ element 10 is reversed, and a state where the magnetization directions of the fixed layer 11 and the recording layer 13 are parallel or antiparallel is created. Here, for example, by defining the parallel state as “1” state and the anti-parallel state as “0” state, binary data writing is realized.

  Next, the read operation is performed as follows using the transistor Tr functioning as a read switching element. A bit line 28 and a read word line (RWL) 22 corresponding to the selected MTJ element 10 are selected, and a read current Ir that tunnels through the nonmagnetic layer 12 of the MTJ element 10 is passed. Here, the junction resistance value changes in accordance with the cosine of the relative angle of the magnetization directions of the fixed layer 11 and the recording layer 13, and the magnetization directions of the fixed layer 11 and the recording layer 13 are in a parallel state (for example, “1” state). Has a low tunnel resistance, and when the magnetization directions of the fixed layer 11 and the recording layer 13 are in an antiparallel state (for example, “0” state), the junction resistance value is high. can get. Therefore, the difference between the resistance values is read to determine the “1” and “0” states of the MTJ element 10.

[2] Selection Diode Type FIG. 18 is a circuit diagram showing a selection diode type MRAM. FIG. 19 is a cross-sectional view showing the memory cell MC of the selection diode type MRAM shown in FIG. In FIG. 18, the space between the semiconductor substrate 21 and the bit line (BL) 28 is filled with an insulating layer (not shown).

  As shown in FIGS. 18 and 19, one memory cell MC of the selected diode type includes one MTJ element 10, a diode D connected to the MTJ element 10, a bit line (BL) 28, and a word line (WL 26). The memory cell array MCA is configured by arranging a plurality of memory cells MC in an array.

  Here, the diode D is a PN junction diode, for example, and is composed of a P-type semiconductor layer and an N-type semiconductor layer. One end (for example, a P-type semiconductor layer) of the diode D is connected to the MTJ element 10. On the other hand, the other end (for example, an N-type semiconductor layer) of the diode D is connected to the word line 26. In the illustrated structure, a current flows from the bit line 28 to the word line 26.

  In addition, the arrangement | positioning location and direction of the diode D can be changed variously. For example, the diode D may be arranged in a direction in which current flows from the word line 26 to the bit line 28. The diode D can also be formed in the semiconductor substrate 21. Furthermore, the diode D can also have the same shape as the MTJ element 10 (for example, a so-called cross shape).

  Further, the MTJ element 10 is arranged such that the easy axis of magnetization is inclined by, for example, 5 degrees (or rotated by 5 degrees) with respect to the extending direction of the word line (WL) 26. In other words, the MTJ element 10 is arranged such that the hard axis of magnetization is inclined by, for example, 5 degrees with respect to the extending direction of the bit line (BL) 28. As the MTJ element 10, for example, an element having the planar shape shown in FIG. 12 is used.

  In the select diode type memory cell MC as described above, the data write operation is the same as that of the select transistor type, and the write currents Iw1 and Iw2 are supplied to the bit line 28 and the word line 26 to thereby fix the fixed layer of the MTJ element 10. 11 and the magnetization direction of the recording layer 13 are made parallel or anti-parallel.

  On the other hand, the data read operation is almost the same as that of the selection transistor type, but in the case of the selection diode type, the diode D is used as a read switching element. That is, by using the rectification of the diode D, the bias of the bit line 28 and the word line 26 is controlled so that the non-selected MTJ element is reverse-biased so that the read current Ir flows only through the selected MTJ element 10. To do.

[3] Crosspoint Type FIG. 20 is a circuit diagram showing a crosspoint type MRAM. FIG. 21 is a cross-sectional view showing the memory cell MC of the cross-point type MRAM shown in FIG. In FIG. 21, the space between the semiconductor substrate 21 and the bit line (BL) 28 is filled with an insulating layer (not shown).

  As shown in FIGS. 20 and 21, one cross-point type memory cell MC is configured to include one MTJ element 10, a bit line (BL) 28, and a word line (WL) 26. . The memory cell array MCA is configured by arranging a plurality of memory cells MC in an array.

  Specifically, the MTJ element 10 is disposed near the intersection of the bit line 28 and the word line 26, one end of the MTJ element 10 is connected to the word line 26, and the other end of the MTJ element 10 is connected to the bit line 28. ing.

  The MTJ element 10 is arranged such that the easy axis of magnetization is inclined, for example, by 5 degrees (or rotated by 5 degrees) with respect to the extending direction of the word line (WL) 26. In other words, the MTJ element 10 is arranged such that the hard axis of magnetization is inclined by, for example, 5 degrees with respect to the extending direction of the bit line (BL) 28. As the MTJ element 10, for example, an element having the planar shape shown in FIG. 12 is used.

  In the cross-point type memory cell MC as described above, the data write operation is the same as that of the selection transistor type, and the write currents Iw1 and Iw2 are supplied to the bit line 28 and the word line 26 to thereby fix the fixed layer of the MTJ element 10. 11 and the magnetization direction of the recording layer 13 are made parallel or anti-parallel. On the other hand, in the data read operation, the data of the MTJ element 10 is read by causing a read current Ir to flow through the bit line 28 and the word line 26 connected to the selected MTJ element 10.

  As described above in detail, according to the present embodiment, a plurality of types of magnetic random access memories (MRAM) can be configured using the MTJ element 10. Note that each type of magnetic random access memory (MRAM) described above is an example, and can be applied to other types of magnetic random access memory (MRAM).

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

The top view which shows one Example of the MTJ element 10 which concerns on this invention. FIG. 2 is a cross-sectional view of the MTJ element shown in FIG. FIG. 2 is a plan view showing a main part of an MRAM including the MTJ element 10 shown in FIG. The figure which shows the asteroid curve of the MTJ element 10 shown in FIG. 1 is a plan view showing a main part of an MRAM including an MTJ element 10 according to a first embodiment of the present invention. The figure which shows the asteroid curve of the MTJ element 10 shown in FIG. The figure which shows the rotation angle dependence of the magnetic field Hc in the MTJ element. The figure which shows the rotation angle dependence of dispersion | variation (sigma) Hc of the magnetic field Hc in the MTJ element. The figure which shows the specific numerical value of the curve shown in FIG. FIG. 5 is a plan view showing a second example of the MTJ element 10. FIG. 6 is a plan view showing a third example of the MTJ element 10. FIG. 6 is a plan view showing a fourth example of the MTJ element 10. FIG. 10 is a plan view showing a fifth example of the MTJ element 10. FIG. 10 is a plan view showing a sixth example of the MTJ element 10. FIG. 6 is a circuit diagram showing a select transistor type MRAM according to a third embodiment of the present invention. FIG. 16 is a plan view showing a configuration of a select transistor type MRAM shown in FIG. 15. FIG. 16 is a cross-sectional view showing a memory cell MC of the select transistor type MRAM shown in FIG. 15. The circuit diagram which shows the selection diode type | mold MRAM which concerns on the 3rd Embodiment of this invention. FIG. 19 is a cross-sectional view showing a memory cell MC of the selection diode type MRAM shown in FIG. 18; FIG. 6 is a circuit diagram showing a cross-point type MRAM according to a third embodiment of the present invention. FIG. 21 is a cross-sectional view showing a memory cell MC of the cross-point type MRAM shown in FIG. 20.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... MTJ element, 10a ... Extension part, 10b, 10c ... Projection part, 11 ... Fixed layer, 12 ... Nonmagnetic layer, 13 ... Recording layer, 14 ... Antiferromagnetic layer, 15 ... 1st write wiring, 16 ... Second write wiring, 21 ... semiconductor substrate, 22 ... gate electrode, 23a ... drain diffusion layer, 23b ... source diffusion layer, 24a, 24b, 24c, 24d ... contact plug, 25a, 25b, 25c ... wiring layer, 26 ... word Line 27, base metal layer, 28 bit line, MC memory cell, MCA memory cell array, Tr transistor, D diode.

Claims (8)

A magnetoresistive effect element including a fixed layer in which the direction of magnetization is fixed, a recording layer in which the direction of magnetization changes, and a nonmagnetic layer provided between the fixed layer and the recording layer;
A first wiring extending in a first direction and generating a magnetic field for recording information on the recording layer of the magnetoresistive element, and
The recording layer is
The first direction extends in a second direction rotated so as to form an angle greater than 0 degrees and not more than 20 degrees with respect to the first direction, and is opposed to each other and extends in the second direction. And an extended portion having a second side surface and third and fourth side surfaces facing each other;
First and second projecting portions projecting from the first and second side surfaces in a third direction perpendicular to the second direction, respectively.
The third and fourth side surfaces are each inclined in a rotation direction in which the extension portion rotates with respect to the third direction. The second direction is a direction along the easy axis direction,
The magnetic storage device according to claim 1, wherein the third direction is a direction along a hard axis direction.   3. The magnetic storage device according to claim 1, wherein the planar shape of the recording layer has a rotational symmetry of 180 degrees and does not have a mirror symmetry. 4.   4. The planar shape of the extension part is a quadrilateral having four corners, one diagonal is an acute angle, and the other diagonal is an obtuse angle. The magnetic storage device described in 1.   The magnetic storage device according to claim 1, wherein the planar shape of the extending portion is a parallelogram.   6. The magnetic storage device according to claim 1, wherein the recording layer has a plurality of rounded corners.   The magnetic storage device according to claim 1, wherein the angle is greater than 0 degree and 15 degrees or less.   A second wiring extending in a fourth direction perpendicular to the first direction and generating a magnetic field for recording information in the recording layer of the magnetoresistive element; The magnetic storage device according to claim 1, wherein the magnetic storage device is a magnetic storage device.

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